#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

#define COMMAND_SIZE 1024
#define FORMAT "[%s@%s %s]# "

// 下面是shell定义的全局数据
// 1. 命令行参数表 
#define MAXARGC 128
char *g_argv[MAXARGC]; // 命令行参数表
int g_argc = 0;

// 2. 环境变量表
#define MAX_ENVS 128
char *g_env[MAX_ENVS];
int g_envs = 0;

// for test
char cwd[1024];
char cwdenv[1024];

// last exit code
int lastcode = 0;

const char *GetUserName()
{
    const char *name = getenv("USER");
    return name == NULL ? "None" : name;
}

const char *GetHostName()
{
    const char *hostname = getenv("HOSTNAME");
    return hostname == NULL ? "None" : hostname;
}

const char *GetPwd()
{
    // const char *pwd = getenv("PWD");
    const char *pwd = getcwd(cwd, sizeof(cwd));
    if (pwd != NULL)
    {
        snprintf(cwdenv, sizeof(cwdenv), "PWD=%s", cwd);
        putenv(cwdenv);
    }
    return pwd == NULL ? "None" : pwd;
}

const char *GetHome()
{
    const char *home = getenv("HOME");
    return home == NULL ? "" : home;
}

// / /a/b/c
std::string DirName(const char *pwd)
{
#define SLASH "/"
    std::string dir = pwd;
    if(dir == SLASH) return SLASH;
    auto pos = dir.rfind(SLASH);
    if(pos == std::string::npos) return "BUG?";
    return dir.substr(pos+1);
}

void MakeCommandLine(char cmd_prompt[], int size)
{
    snprintf(cmd_prompt, size, FORMAT, GetUserName(), GetHostName(), DirName(GetPwd()).c_str());
    //snprintf(cmd_prompt, size, FORMAT, GetUserName(), GetHostName(), GetPwd());
}

void PrintfCommandPrompt()
{
    char prompt[COMMAND_SIZE];
    MakeCommandLine(prompt, sizeof(prompt));
    printf("%s", prompt);
    fflush(stdout);
}

bool GetCommandLine(char *out, int size)
{
    
    char *c = fgets(out, size, stdin); 
    if(c == 0) return false;
    out[strlen(out)-1] = 0; //清理\n
    if(strlen(out) == 0) return false;
    return true;
}

bool CommandParse(char *commandline)
{
#define SEP " "
    g_argc = 0;
    // 命令行分析 "ls -a -l" -> "ls" "-a" "-l"
    g_argv[g_argc++] = strtok(commandline, SEP);
    while(g_argv[g_argc++] = strtok(nullptr, SEP));
    g_argc--; // 会把NULL也算成一段
    return g_argc > 0 ? true : false;
}

void PrintfArgv()
{
    for(int i = 0; g_argv[i]; i++)
    {
        printf("argv[%d]->%s\n", i, g_argv[i]);
    }
    printf("argc:%d\n", g_argc);
}

void InitEnv()
{
    extern char **environ;
    memset(g_env, 0, sizeof(g_env));
    g_envs = 0;
    // 本来要从配置文件来
    for (int i = 0; environ[i]; i++)
    {
        // 1.1 申请空间
        g_env[i] = (char*)malloc(strlen(environ[i]) + 1);
        strcpy(g_env[i], environ[i]);
        g_envs++;
    }
    g_env[g_envs++] = "Ciallo=for_test";// 测试
    g_env[g_envs] = NULL;
    // 2.导成环境变量
    for (int i = 0; g_env[i]; i++)
    {
        putenv(g_env[i]);
    }
}

bool Cd()
{
    if (g_argc == 1)
    {
        std::string home = GetHome();
        if(home.empty()) return true;
        chdir(home.c_str());
    }
    else
    {
        std::string where = g_argv[1];
        if (where == "-")
        {
            //...
        }
        else if (where == "~")
        {
            //...
        }
        else
        {
            chdir(where.c_str()); 
        }
    }
    return true;
}

void Echo()
{
    if (g_argc == 2)
    {
        // echo "Ciallo~"
        // echo $?
        // echo $PATH
        std::string opt = g_argv[1];
        if (opt == "$?")
        {
            std::cout << lastcode << std::endl;
            lastcode = 0;
        }
        else if (opt[0] == '$')
        {
            std::string env_name = opt.substr(1);
            const char *env_value = getenv(env_name.c_str());
            if (env_value)
                std::cout << env_value << std::endl;
        }
        else
        {
            std::cout << opt << std::endl;
        }
    }
}

bool CheckAndExecBulitin()
{
    std::string cmd = g_argv[0];
    if (cmd == "cd")
    {
        Cd();
        return true;// 是内键命令
    }
    else if (cmd == "echo")
    {
        Echo();
        return true;
    }
    else if (cmd == "export")
    {
        //...
    }
    return false;
}

int Execute()
{
    pid_t id = fork();
    if(id == 0)
    {
        // 子进程
        execvp(g_argv[0], g_argv); 
        exit(1);
    }
    int status = 0;
    // 父进程
    pid_t rid = waitpid(id, &status, 0);
    //(void)rid; // rid使用一下
    if(rid > 0)
    {
        lastcode = WEXITSTATUS(status);
    }
    return 0;
}

int main()
{
    // shell 启动时，从系统中获取环境变量
    // 我们的环境变量信息应该从父shell统一来
    InitEnv();
    
    while(true)
    {
        // 1. 输出命令行提示符
        PrintfCommandPrompt();
        
        // 2. 获取用户输入的命令
        char commandline[COMMAND_SIZE];
        if(!GetCommandLine(commandline, sizeof(commandline)))
            continue;
        
        // 3. 命令行分析 "ls -a -l" -> "ls" "-a" "-l"
        if(!CommandParse(commandline))
            continue;
        //PrintfArgv();
        
        // 4. 检测处理内键命令
        if(CheckAndExecBulitin())
            continue;


        // 5. 执行命令
        Execute();    
        
    }
    return 0;
}
